In the past year two major advances were made in our research effort toward obtaining optical signal from SR and toward development of an optical voltage clamp system. We have developed a chemically skinned mammalian ventricular preparation which responds to Ca-induced Ca release. These fibers 50-100 micrometer in diameter can be stained with voltage-dependent dyes such as Merocyanine Oxazolone. In the absence of the surface membrane an optical signal can be monitored which occurs with contractile oscillations. The optical signal often precedes the contraction signal and is as yet not clear whether it is purely a voltage signal. We intend to investigate the ionic and drug dependence of this signal. Wave splitting and overstretch will be used to suppress the motion artifact. The development of the optical voltage clamp system is still in the instrumentation phase. We have carried out preliminary experiments to show that it is quite possible to feed back the optical signal and control the membrane potential. Technical developments are proceeding in the direction of maximizing homogenous distribution of light in the ventricular strips. For this purpose we have utilized a parabilla which allows light to be focused at its center. The muscle is then placed in the hole drilled at the center of the parabilla. We are hopeful that such a technique will optimize the distribution and collection of light from a multicellular tissue.